His other alleged crime was "illegally obtaining citizens' personal information," Beijing police said on their official microblog, adding that the investigation into Pu is still ongoing.

Pu, 49, was detained in early May after attending a low-key seminar in a private home to mark the 25th anniversary of the Tiananmen Square massacre. State-run Global Times newspaper said in an editorial at the time that he had crossed "a legal red line" by associating himself with a topic still considered taboo in China.

Pu took part in the student-led demonstrations in 1989 that ended in a bloody military crackdown on June 4 of that year. He later become one of the best-known lawyers in China for defending human rights in courts as well as in the media. --

Pu's arrest comes as the latest development in a new wave of government crackdowns on human rights advocates. Police put nearly 100 people in detention or under house arrest before this year's Tiananmen anniversary, said Chinese Human Rights Defenders, a Washington-based monitoring group.

When President Xi Jinping took office in 2013, some activists hoped he would preside over a system more tolerant of dissent and discussion. His government, however, is now widely seen as tightening the screws on the work of activists and intellectuals, including the sentencing of Xu Zhiyong, another well-known human rights lawyer, to four years in prison in January after he pushed for financial transparency for senior officials.